1. Field of the Invention
The present invention relates to optical devices, optical scanning devices, image forming apparatuses, and manufacturing methods of optical devices. More specifically, the present invention relates to an optical device in which an optical element is held by a package member, an optical scanning device including the optical device, an image forming apparatus including the optical scanning device, and a manufacturing method of the optical device.
2. Description of the Related Art
In recent years and continuing, optical elements have been practically applied and used in various types of optical equipment. Examples of optical elements are a light receiving element such as a CCD sensor and a CMOS sensor, a light emitting element such as a surface-emitting laser, an optical scanner element using an MEMS mirror, and an optical switching element.
For the purpose of improving efficiency, these optical elements are typically used in a two-dimensional array. When optical elements are used in a two-dimensional array, the number of signal lines increases. Hence, it is difficult to accommodate the optical elements in a typical CAN package, and therefore the optical elements are typically accommodated in a ceramic package.
The ceramic package accommodating the optical elements is sealed in an airtight manner with a translucent lid member made of a material such as glass or sapphire, to achieve environmental resistance.
Conventionally, the ceramic package and the lid member are joined together by a hermetic seal (see, for example, patent document 1), by soldering (see, for example, patent document 2), etc.
In recent years and continuing, for the purpose of reducing cost, resin (resin adhesive) is increasingly used for joining together the ceramic package and the lid member (see, for example, patent document 3).
Patent document 4 discloses a package in a semiconductor device formed as follows. Specifically, a recessed portion is formed on the top surface of the package body accommodating a semiconductor element. A cap is fit into the recessed portion, and sealing glass is applied around the cap to seal the package body in an airtight manner. In this package of a semiconductor device, the recessed portion has substantially the same size as the cap. Furthermore, the recessed portion has leading-in parts extending outwards, provided at plural positions along the periphery of the recessed portion.
In a conventional ceramic package, a recessed portion is provided on the surface of the ceramic package, so that the lid member can be adhered to an appropriate position. The size of the recessed portion is determined such that the gap between the recessed portion and the lid member is minimized.
When resin is used for joining together the ceramic package and the lid member, the resin has a tendency of protruding outside the ceramic package. Consequently, the appearance of the product may be degraded. Furthermore, the protruding resin may break off as a result of contacting other objects in the process of distributing or using the ceramic package. When the resin breaks off, the airtightness of the ceramic package may be degraded, depending on the extent of the resin that has broken off.
Furthermore, the protruding resin may be obstacles when assembling an optical system with lenses on the ceramic package.
The resin may be prevented from protruding outside by reducing the amount of resin used. However, it is difficult to control the amount of resin in the manufacturing process. If the amount of resin is too small, the ceramic package may not be appropriately sealed in an airtight manner. Furthermore, resin basically has a moisture-permeable feature, and thus lacks resistance to high temperature and high humidity. Therefore, it is necessary to increase the sealing width (area of adhering resin) for the purpose of enhancing the resistance to high temperature and high humidity. This makes it even more difficult to control the amount of resin.
One approach is to increase the size of the gap between the recessed portion and the lid member. However, this may degrade the precision in positioning the lid member.
The inventors of the present invention made a product with reference to the package in a semiconductor device disclosed in patent document 4. The inventors formed a recessed portion on the package having substantially the same size as the lid member, formed leading-in parts extending outwards provided at plural positions along the periphery of the recessed portion, and joined the lid member to the recessed portion with the use of resin. As a result, it was found that resin protruded outside at parts where there are no leading-in parts, and therefore, the quality of the product was not good.
Patent Document 1: Japanese Laid-Open Patent Application No. 2004-228549
Patent Document 2: Japanese Laid-Open Patent Application No. 2005-329532
Patent Document 3: Japanese Laid-Open Patent Application No. 2001-267681
Patent Document 4: Japanese Patent No. 2674214